Numerous borehole logging methods and tools are known to provide many kinds of borehole data. One important aspect of borehole logging is the physical alignment of the tool with the borehole. Operation of some types of borehole tools require centralization of the tool in the wellbore, operation of other types of borehole tools require eccentric positioning in the wellbore, and other types of borehole tools are preferentially operated when in contact with the wellbore surface.
Apparatuses are known to position a borehole tool centrically, eccentrically, or in other preferential alignment within a wellbore. A positioning apparatus also may be used to position a borehole tool at a preferred distance from the surface of the wellbore perimeter or to position a borehole tool against the wellbore perimeter surface. The use of a positioning apparatus may be particularly important when the borehole tool is sensitive to the tool standoff, the offset between the tool and the wall of the well bore. Types of apparatus known to be used for positioning include linked arm, leaf spring, bow spring, coil spring and various combinations thereof.
Positioning a borehole tool within a wellbore can be difficult. Some wellbores may be irregular when drilled. In others, the wellbore perimeter surface configuration may be affected by collapse, encroachment, or wash-out of earth formations. These conditions result in a wellbore that is not ideally circular or uniform. Similarly, in a deviated well the wellbore varies from uniformly circular owing to non-vertical geometry. Often boreholes having a non-circular perimeter are referred to as having a “short-axis” and a “long-axis”. Known symmetric positioning devices are poorly adapted to use in wellbore having a non-circular or non-uniform perimeter. Thus an apparatus capable of positioning a borehole tool in a non-circular or non-uniform wellbore, as well as a circular or uniform wellbore is desirable.
Some well logging sondes, such as those providing density or microresistivy measurements, are equipped with extra springs to ensure contact of sensor pads with the wellbore. In these sondes, the springs may be arranged so that the potential energy of the total spring system is minimized when the sonde is aligned along the “short axis” of the wellbore. Such known systems have limitations however as they are not adjustable nor can the system performance or contact pressure able to be monitored.
When logging in a borehole, it is useful to know the wellbore size and configuration. Methods are known to estimate wellbore size by processing and interpreting data acquired by logging tools or by estimating borehole size from information such as drill bit size, drilling rate, fluid pressure and expected formation parameters. These methods however provide an estimate rather that a direct measurement. Direct measurement of borehole size using mechanical or acoustic calipers is known. But the expense and effort required to log a borehole with a separate caliper is disadvantageous. A positioning apparatus that can provide direct measurements of the borehole during logging tool operation would provide operational advantages.
When performing logging operations with multiple logging tools disposed in a borehole on same tool string, some tools may require centralization while other tools may require a different preferred alignment in the wellbore. In other situations, it may be desired to log a borehole more that once, using the same borehole tool with different alignments in the borehole. It would be expedient for well site operations if the same apparatus could be configured and used to provide various preferred alignments of a logging tool in a borehole. It would be advantageous for operations if a plurality of the same positioning apparatus could be used to position a plurality of borehole tools in a tool string. It would be particularly useful if one of the plurality of positioning apparatus could be configured centralize a tool while another of the plurality of positioning apparatus could be configured to another tool eccentrically in the borehole. A positioning apparatus that can be configured and used flexibly to position as desired in a borehole is needed.
In deviated wells, proper alignment of a borehole tool in a wellbore can be particularly difficult as the wellbore typically varies from uniformly circular owing to its non-vertical geometry. In addition, in a deviated wellbore, the weight of the borehole tool itself will tend to position the tool off-center. Known symmetric positioning devices are poorly adapted for use in non-vertical boreholes. Thus an apparatus capable of positioning a borehole tool in circular and non-circular wellbore is desirable.